My main question is: Does he act this way with your trainer?
But this sounds like he has zero respect for you. I doubt he learned the basics though, as a pasture ornament, so with this horse, I would start from the bottom up- beginning of training. Teach him to respect your space, first. If he wants to run up to you in the field, he needs to stop a certain distance away, and stand for YOU to come to HIM. Try walking into the pen, and when he charges to you, swing the lead rope and make him lounge around, away from you. If he wants to run, he'll get to run. After he brings himself to a stop, walk up to him. If he moves, stop. If he stops, walk again, until you get to him. Rub on him, scratch his head, show him that that's what you want. Then turn around and walk away. No halter, no taking him out to work, just do this for however long it takes. This is just what I would do, ask your trainer if this method is something they want to try first- If your trainer has an agenda, you probably don't want to mess that up. I know how difficult that can be, lol.